In an attempt to verify the feasibility of the use of the proposed isotope probes (L-{1-13C, methyl-2H3} methionine, and L-3,3-H2- cysteine), three volunteers were studied during the reporting period using the 3-hour primed continuous infusion approach. The data suggest that additional work needs to be done to assure stability of the derivatives prepared for GCMS analysis. Volunteers tolerated the studies well.